Method for automatically measuring elementary time unit for communication peripherals dedicated to smart cards

ABSTRACT

A process for automatically measuring the unit of time (ETU=Elementary Time Unit) for communication peripherals dedicated to smart cards during a dialogue between a reader and the smart card, so as to configure the reading device. This process consists in taking account of the descending front of the start bit, taking account of the ascending front of the start bit, and measuring the time between the descending and ascending fronts, which permits the automatic calibration of the communication processor.

FIELD OF THE INVENTION

The present invention relates to a process for measuring the time unit(ETU=Elementary Time Unit) during a dialogue between a reader and asmart card, so as to configure the reading device.

The state of the art at present proposes a technique of sampling of thefirst octet or character, then a calibration by means of software.

During the start-up of a dialogue between a reader and a smart card, thereading device must be configured to sample the data transmitted inseries or in an asynchronous fashion by the card (width of eachtransmitted bit=1 ETU).

To the nearest decimal point, the width of each bit is ETU=372 CLK,namely 1/9600 second for a card timed to 3.57 megahertz (MHz). However,certain cards have a value to the nearest decimal point of 512 CLK.

There is known from EP-A-0 347 894 a card with integrated circuitshaving recognition means (22) to determine whether the charged card (23)has an identifiable frequency.

However, only a limited number of frequencies can be identifiedaccording to this technique.

There is also known from the Patent Abstract of Japan JP 04-319756, aninterface of a communication series adapted to reconstitute thefrequency of transmission in the connection series.

According to the invention, a processor for measuring the time unitduring start-up of the dialogue permits operating in a transparentmanner with cards having ETUs that are different to the nearest decimalpoint.

The old techniques of sampling require considerable time and use forthat purpose a microprocessor. The invention permits increasing thespeed of taking account of the time unit by not using software, butrather conventional computer hardware.

SUMMARY OF THE INVENTION

To this end, the present invention relates to a process for measuringthe time unit (ETU=Elementary Time Unit) during a dialogue between areader and a smart card, so as to configure the reading device,characterized in that it consists:

in taking account of the descending front of the start bit,

taking account of the ascending front of said start bit, and

measuring the time between said descending and ascending fronts,

which permits the automatic calibration of the communication processor.

The measured time corresponds to the low level of the start bit.

The time is measured as a number of cycles of the card clock.

The automatic calibration consists:

in defining the value of a half unit of time,

carrying over this value after the ascending front of the start bit todefine the middle of the following bit,

carrying over successively the value of a time unit to define theposition of each successive bit.

The processor can be used with different values of the time unit, suchas ETU=372 CLK or ETU=512 CLK.

This process, in which the first character is constituted by the startbit (low level during a unit of time) then a so-called time sharing bitor TS (high level during the unit of time) is characterized in thatafter the TS bit, it is possible to reprogram or to adjust the value ofthe unit of time measured.

The processor permits the elimination of parasitic signals, which is tosay values of the time unit that are too small.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process for measuring the time unitwhich regulates the exchanges between a reader and a smart card.

This process thus permits configuring the reading device no matter whatthe value of the unit of value.

During start-up of the dialog (ATR: Answer To Reset), the calibration ofthe time unit or ETU, takes place automatically with reception of thefirst character TS which is defined by the standard.

No matter what the convention (direct or the reverse), this characterhas the characteristic of being comprised by a start bit.

This start bit is constituted by a transition from 1 toward 0, then astabilization at 0 during an ETU, finally to return to the high levelfor at least one ETU.

The communication processor, which comprises means permitting the use ofthe process according to the invention, will thus be automaticallycalibrated by the measurement of the time between the descending front,transition from 1 to 0, of the start bit and the rising front, 0 to 1,again of this start bit.

This time measured in numbers of clock cycles of the smart card is equalto the ETU of the card. The clock operates of course with the help of aquartz system.

The value of the ETU is then used to sample the rest of the bitsconstituting the character TS.

At the end of reception of the TS, it is possible to reprogram and toadjust the measured value of the ETU.

Moreover, this processor is designed to eliminate parasitic signals whenthe values of the time unit are too small.

This invention has the advantage of permitting dialogue in a transparentmanner with cards working at standardized rates that are different ornot.

The automatic calibration therefore consists in defining the value of ahalf unit of time which will have been computed between the descendingfront and the ascending front of the start bit, then carrying over thisvalue after the front of the start bit to define the middle of thefollowing bit.

Once this is done, the position is located in plane right in the middleof the value of the following bit and it will then suffice to carry oversuccessively the value of one time unit to define the position of eachsuccessive bit.

Thanks to this technique, the processor will be able to adapt todifferent values of the time unit no matter what the configuration used.

In the most common case, the value of the time unit could be 372 CLK or512 CLK.

Nevertheless, it is always possible that other values will appear infuture standards.

A smart card used can be according to the standard ISO 7916-3.

This type of smart card operates in an asynchronous fashion, hence theinterest of the process according to the invention.

What is claimed is:
 1. Process for measuring a time unit during adialogue between a reader and a smart card, so as to configure thereader, said time unit corresponding to a length of a bit transmitted inseries by the card to the reader, characterized in that said processconsists: in taking into account a descending front of start bittransmitted by the card to the reader, taking into account an ascendingfront of said start bit, and measuring the time between said descendingand ascending fronts, in numbers of cycles of the card clock, to carryout an automatic calibration of the communication processor of thereader with said measured time.
 2. Process according to claim 1,characterized in that the measured time corresponds to a low level ofthe start bit.
 3. Process according to claim 1, characterized in thatthe time is measured in numbers of clock cycles of the card.
 4. Processaccording to claim 1, characterized in that the automatic calibrationconsists: in defining the value of a half unit of time, in carrying overthis value after the ascending front of the start bit to define themiddle of the following bit, successively carrying over a value of aunit of time to define the position of each successive bit.